Method for determining the concentration of contamination on a component

ABSTRACT

Methods for determining the location of a droplet of water placed on a surface of a semiconductor wafer and for determining the concentration of contamination on a semiconductor wafer surface. One method includes placing a droplet of liquid on the semiconductor wafer surface and generating reference indicia indicative of a location of the droplet on the surface. Another method includes establishing first and second reference axes that intersect at a point and superimposing the point over a droplet of water on the semiconductor wafer surface. A first reference coordinate indicative of the position of the point along the first axis and a second reference coordinate indicative of the position of the point along the second axis are generated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/316,233, filed May 21, 1999, now U.S. Pat. No. 6,242,271, issued Jun.5, 2001, which is a divisional application of U.S. patent applicationSer. No. 08/979,894, filed Nov. 26, 1997, now U.S. Pat. No. 5,961,722,issued Oct. 5, 1999.

FEDERALLY SPONSORED RESEARCH

Not applicable.

BACKGROUND OF THE INVENTION

The subject invention relates generally to locating a reference pointand, more particularly, to establishing reference coordinates for thelocation of a dried droplet of liquid on a semiconductor wafer forassessing the purity of the wafer surface.

Integrated circuits are solid state devices in which electricalcomponents and electrical connections between components areincorporated into a solid matrix by the strategic placement of variousconducting, semiconducting and insulating materials. The development ofthe integrated circuit has led to the miniaturization of electronics byproviding a strong matrix to support and protect fragile miniaturizedcomponents and connections and by facilitating the placement of theelectrical components in close proximity. The integrated circuit hasfurther served to increase the reliability of electronic devices by theelimination of moving parts and fragile electrical wiring andconnections.

Integrated circuits are typically mass produced by forming hundreds ofcircuits called “dice” on a semiconductor substrate known as a “wafer”.The circuits are formed by depositing a series of individual layers ofpredetermined materials on the wafer. The individual layers of theintegrated circuit-are produced by a series of manufacturing steps. Theprecise characteristics of the layers, such as composition, thickness,and surface quality uniquely determine the electronic properties and theperformance of the integrated circuit.

Successful fabrication of large scale integrated silicon circuits isdependent upon the purity of the wafer surfaces. The presence of metalcontaminates such as iron, nickel, copper and zinc on the semiconductorsurfaces can lead to defects during high temperature processing of thewafers because those contaminates can diffuse into the semiconductormaterial. In an effort to monitor the purity of the semiconductorsurfaces, highly sensitive methods for analyzing surface purity havebeen developed.

One method for determining the concentration of contamination on asilicon wafer is-known as vapor phase decomposition or “VPD”. Suchmethod involves supporting the wafer in a specially designed deviceknown as a VPD reactor. A VPD reactor typically contains anacid-resistant beaker and platforms for supporting wafers within achamber. The wafer platforms are typically water-cooled and the beakersare generally heated by a heat exchanger arrangement integrated into thebottom of the reactor.

After the wafers are placed onto the wafer platform, a solution ofhydrofluoric acid is added to a beaker. The hydrofluoric acid is heatedwithin the beaker which causes it to vaporize within the chamber. Theacid vapor permeates the chamber and dissolves the silicon oxide surfacelayer on the wafer. The wafer is cooled by the support platform whichcauses a thin film of moisture to condense on the wafer surface. Theimpurities on the surface of the wafer are contained in the moisturefilm.

The wafer is then removed from the reactor and a predetermined amount ofdeionized water is then immediately pipetted on to the surface. Thisdroplet is then moved over the entire surface area by gently tilting thewafer. During this process, the impurities are collected in the droplet.The droplet is then moved generally to the center of the wafer and thewafer is placed into a vacuum chamber wherein the droplet is dried onthe wafer. After the droplet has been dried, its contents are analyzedby a process known as total reflection X-ray spectrometry (“TXRF”). Theprinciple of TXRF is based on the detection of trace elements on thesurface of an optically flat substrate by their characteristic X-raysexcited by an incoming X-ray beam in total external reflection geometry.Through use of this process, the presence of iron, nickel, copper andzinc on the wafer surface can be detected.

In the past, the location of the droplet of water on the wafer wasapproximated. Because the exact location of the droplet was unknown,accurate positioning of the TXRF machine relative to the water dropletwas time consuming. Moreover, although some TXRF machines are capable ofaccepting coordinates of a point of interest relative to the machinehead, prior methods lacked the capability of generating such coordinatesfor use by the X-ray machine.

Thus, there is a need for an apparatus and method for generatingreference coordinates for a position on a component such as a wafer thatcan be used to accurately orient a device such as an X-ray machinerelative to the position.

There is a further need for an apparatus having the above-mentionedattributes that is relatively inexpensive to manufacture.

There is yet another need for an apparatus having the above-mentionedattributes that is relatively portable and easy to use.

SUMMARY OF THE INVENTION

In accordance with a particularly preferred form of the presentinvention, there is provided an apparatus for establishing a referencecoordinate for a point on a component. The invention preferably includesa component carriage that has coordinate indicia thereon. A locatorplate is movably supported relative to the component support carriage.The locator plate is provided with reference indicia for registrationwith a point within the carriage and alignment with the coordinateindicia on the component carriage. The invention may further includeabase to which the component carriage and locator plate are movablyattached.

The present invention provides solutions to the aforementioned problemsassociated with prior locator methods and apparatuses and, inparticular, with those methods and apparatuses employed in connectionwith the evaluation of surface contaminates on silicon wafers. Thesubject invention is also relatively inexpensive to manufacture, is easyto use and is portable. Those of ordinary skill in the art will readilyappreciate that these and other details, features and advantages willbecome further apparent as the following detailed description of thepreferred embodiments proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying Figures, there are shown present preferredembodiments of the invention wherein like reference numerals areemployed to designate like parts and wherein:

FIG. 1 is an isometric view of a preferred location device of thepresent invention;

FIG. 2 is an isometric view of the location device of FIG. 1, supportinga silicon wafer thereon;

FIG. 3 is a plan view of the location device of FIG. 2; and

FIG. 4 is a side elevational view of the location device depicted inFIGS. 2 and 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings for,the purposes of illustrating thepresent preferred embodiments of the invention only and not for thepurposes of limiting the same, FIGS. 1-4 show a preferred locationdevice 10 for supporting a component such as a silicon wafer 12 thereon.Although the subject invention is particularly well-suited for use inconnection with silicon semiconductor wafers, the skilled artisan willreadily appreciate that the subject invention could be easily adaptedfor use in connection with a variety of other types of articles andcomponents without departing from the spirit and scope of the presentinvention.

As can be seen in FIGS. 1 and 2, the location device 10 preferablycomprises abase 16 that movably supports a component or wafer carriage40 and a transparent's locator plate. 60. In a preferred form, the base16 includes two side members 18 fabricated from stainless steel or othersuitable material. A pair of spaced rods 20 are attached to the sidemembers 18 and extend therebetween. As will be discussed in furtherdetail below, rods 20 define a first plane along which the componentcarriage 40 can be selectively positioned. The linear directions inwhich the component carriage 40 can move within the first plane aredefined by a first linear axis “X—X”.

Each side member 18 has a longitudinally extending notch 24 forreceiving a corresponding lateral rod 26. Lateral rods 26 serve tomovably support the locator plate 60 along a second plane that ispreferably above and parallel to the first plane. The directions inwhich the locator plate 60 can move within the second plane are definedby a second linear axis “Y—Y” that is perpendicular to the “X—X” axis,in a manner that will be discussed in further detail below.

Component carriage 40, in a preferred form, comprises a base plate 41,two side members 42 and an end member 44. The base plate 41 and endmember 44 are preferably attached to the side members 42 by screws suchthat the side members 42 are supported in spaced relation to each other.In this embodiment, the side members 42 are notched to laterally supporta component such as a silicon wafer 12 thereon. See FIG. 2. In apreferred embodiment, commercially available bearings are installed incorresponding bores 45 provided through the side members 42 as shown inFIGS. 1 and 2. The skilled artisan will appreciate that the bearings 46have a bore 48 therethrough for slidably receiving a corresponding rodto slidably support the component carriage 40 between the side members18.

Also in a preferred embodiment, a support frame assembly 62 is providedto movably support the transparent locator plate 60 on the base 16.Preferably, locator plate 60 is fabricated from tempered glass. However,other transparent material could be successfully employed.

Frame assembly 62 preferably comprises a pair of end members 64 and apair of side members 66 that are interconnected by screws (not shown) ina shape that is complementary to the shape of the locator plate 60. Theside members 66 are preferably “L”-shaped for receiving a correspondingedge of the locator plate 60 as shown in FIGS. 1 and 2. Attached to eachcorner of the frame assembly 62 are bearing blocks 70. Each bearingblock 70 is preferably fabricated from stainless steel or other suitablematerial and has a bearing 72 installed therein. Each bearing 72 has abore 74 for slidably receiving a corresponding rod 26 therethrough.Those of ordinary skill in the art will appreciate that the bearingblocks 70, in cooperation with the rods 26 serve to movably support theframe assembly 62 and locator plate 60 for selective travel along axis“Y—Y”. Referencing indicia 80, preferably in the form of crossed lines(82, 84) is provided on the locator plate 60 which can be used toreference a specific point or location on the wafer. Reference scales 86containing coordinate indicia 81 (preferably numerical in nature) arealso preferably attached to at least one side member 42 and the endmember 44 of the component carriage 40. Such referencing coordinateindicia 81 are arranged on the end member 44 and the side member 42 tolie along intersecting axes “A—A” and “B—B”, respectively. See FIGS. 2and 3.

Use of the subject invention 10 in connection with locating a specificreference point such as the location of a water droplet on a wafer 12will now be described. After the water droplet has been dried on thewafer 12, the wafer 12 is placed onto the wafer carriage 40 of thesubject invention. The carriage 40 and/or the locator plate 60 are movedas necessary along the “X—X” and “Y—Y” axes, respectively to bring thepoint where the lines (82, 84) cross into registration with the waterdroplet. After the point where the crossed lines (82, 84) intersect isbrought into registration with the water droplet, X and Y coordinatesfor the droplet location are established wherein the reference lines(82, 84) intersect the coordinate indicia on the scales mounted to theside member 42 and end member 44 of the component carriage 40.

Those of ordinary skill in the art will appreciate that such coordinatescan be used in conjunction with known control systems to locate a pieceof equipment, such as an X-ray machine relative to the water droplet.The skilled artisan will further appreciate that the positioning of thecomponent carriage 40 and the locator plate 60 relative to the basestructure 16 can be automatically established by utilizing, for example,by positioning apparatuses such as lead screws/ball screws and steppermotor arrangements. Also, commercially available sensor arrangementscould be employed to detect the final position of the carriage, thelocator plate and referencing indicia thereon and such data could beincorporated into a control system for controlling the position of othermachinery components relative thereto.

Thus, from the foregoing discussion, it is apparent that the presentinvention provides significant improvements over prior methods forlocating a point of interest on a component such as a silicon wafer. Thesubject invention also provides the advantages of being readily portableand easy to use and cost-effective to manufacture. Those of ordinaryskill in the art will appreciate that various changes in the details,materials and arrangement of parts which have been herein described andillustrated in order to explain the nature of the invention may be madeby the skilled artisan within the principle and scope of the inventionas expressed in the appended claims.

What is claimed is:
 1. A method for determining the concentration ofcontamination on a semiconductor wafer surface, comprising: forming acontamination-collecting droplet of liquid on the semiconductor wafersurface; generating reference indicia indicative of a location of thedroplet of liquid on the semiconductor wafer surface; directing acontamination analyzer to the location of the droplet; and detecting theconcentration of contaminants in the droplet with the contaminationanalyzer.
 2. The method of claim 1 wherein said generating referenceindicia comprises generating a reference coordinate corresponding to alocation of the droplet along a first axis.
 3. The method of claim 2wherein said generating reference indicia comprises generating anotherreference coordinate corresponding to a location of a droplet along asecond axis.
 4. The method of claim 3 wherein the second axis intersectsthe first axis.
 5. The method of claim 2 wherein said generating areference coordinate comprises superimposing the first axis over thedroplet and assigning a coordinate indicative of the location of thedroplet along the first axis.
 6. The method of claim 3 wherein saidgenerating a reference coordinate further comprises superimposing thesecond axis over the droplet and assigning a second coordinate indicateof the location of the droplet along the second axis.
 7. A method fordetermining the concentration of contamination on a semiconductor wafersurface, comprising: collecting impurities in a moisture film on thesemiconductor wafer surface; placing a droplet of liquid on thesemiconductor wafer surface; drying the droplet of liquid on thesemiconductor wafer surface; generating reference coordinates for thedried droplet of water indicative of a location of the dried droplet ofwater on the semiconductor wafer surface: directing a contaminationanalyzer to the location of the droplet; and detecting the concentrationof contaminants in the droplet with the contamination analyzer.
 8. Themethod of claim 7 wherein said collecting comprises: dissolving asilicone oxide layer on the semiconductor wafer surface; and condensingthe moisture film on the semiconductor wafer surface.
 9. The method ofclaim 8 wherein said dissolving, comprises: placing the semiconductorwafer into a chamber; and vaporizing hydrofluoric acid within thechamber.
 10. The method of claim 8 wherein said collecting furthercomprises cooling the wafer within the chamber.
 11. The method of claim7 further comprising moving the droplet over the semiconductor wafersurface.
 12. The method of claim 11 wherein said moving comprisestilting the semiconductor wafer.
 13. The method of claim 7 wherein saiddrying comprises: placing the semiconductor wafer into a vacuum chamber;and operating the vacuum chamber.
 14. A method for determining theconcentration of contamination on a semiconductor wafer surface,comprising: supporting the semiconductor wafer within a chamber;vaporizing an acid within the chamber; cooling the semiconductor wafer;removing the semiconductor wafer from the chamber; placing a droplet ofliquid onto the semiconductor wafer surface; moving the droplet on thesemiconductor wafer surface; placing the semiconductor wafer into avacuum chamber; operating the vacuum chamber to dry the droplet ofliquid at a location on the semiconductor wafer surface; generatingreference indicia for the dried droplet of water indicative of thelocation of the dried droplet of water on the semiconductor wafersurface; directing a contamination analyzer to the location of thedroplet; and detecting the concentration of contaminants in the dropletwith the contamination analyzer.
 15. The method of claim 14 wherein saidgenerating reference indicia comprises generating a reference coordinatecorresponding to a location of the droplet along a first axis.
 16. Themethod of claim 15 wherein said generating reference indicia comprisesgenerating another reference coordinate corresponding to a location of adroplet along a second axis.
 17. The method of claim 16 wherein thesecond axis intersects the first axis.
 18. The method of claim 15wherein said generating a reference coordinate comprises superimposingthe first axis over the droplet and assigning a coordinate indicative ofthe location of the droplet along the first axis.
 19. The method ofclaim 16 wherein said generating a reference coordinate furthercomprises superimposing the second axis over the droplet and assigning asecond coordinate indicate of the location of the droplet along thesecond axis.